1. Technical Field
The present invention relates to a liquid-jet apparatus for ejecting liquid droplets from nozzle openings, and more specifically, to a liquid-jet apparatus capable of ejecting liquid droplets from nozzle openings on the basis of driving pulses.
2. Related Art
In ink-jet recording apparatuses (a kind of liquid-jet apparatus), such as ink-jet printers and ink-jet plotters, while a recording head (head member) is moved in the main scanning direction and a recording sheet (a kind of medium to be printed upon) is moved in the sub-scanning direction, ink droplets are discharged from nozzle openings of the recording head, thereby forming images (characters) on the recording sheet. For example, a pressure generating chamber communicating with the nozzle openings is compressed or decompressed to eject the ink droplets.
For example, the deformation of a piezoelectric vibrator is used to compress or decompress the pressure generating chamber. In the recording head, the piezoelectric vibrator is deformed in accordance with a driving pulse supplied. The deformation of the piezoelectric vibrator causes the volume of the pressure chamber to vary, and the variation in the volume of the pressure chamber causes ink droplets to be ejected from the nozzle openings.
In the recording apparatus, a driving signal, which is a periodic signal having pulse waveforms, is generated. Meanwhile, ejecting data (gray-scale data) is transmitted to the recording head. Only necessary pulse waveforms are selected from the driving signal on the basis of the transmitted ejecting data, and the selected pulse waveforms are supplied to the piezoelectric vibrator. That is, the ejecting of the ink droplets from the nozzle openings is controlled by the ejecting data.
When the ink droplets are ejected with the recording head in an off state, the ink droplets drop to positions directly below the nozzle openings. However, in general, the ink droplets are ejected while the recording head is moving in order to print images at high speed. The ink droplets ejected from the recording head while the recording head is moving drop at positions deviating from the positions that are directly below the nozzle openings due to inertia caused by the movement of the recording head.
For example, the inventors have proposed a technique for improving the accuracy of recording in consideration of the deviation between actual and intended ink drop positions (JP-A-2002-264307). In JP-A-2002-264307, the inventors have proposed a technique for adjusting the phase of each driving pulse on the basis of the ejecting speed of ink droplets, which is a measured value obtained corresponding to piezoelectric vibrators of nozzle openings and ink characteristics, in order to markedly improve the accuracy of recording, paying attention to the deviation between actual and intended ink drop positions.
However, the inventors found that the ejecting speed of ink droplets obtained corresponding to the piezoelectric vibrators of the nozzle openings and the ink characteristics varied in accordance with the ejecting state of ink to the previous pixel (the ejecting of ink in a previous printing period). The inventors investigated the cause and came to the following conclusion. That is, after an ink droplet is ejected from the nozzle opening, the meniscus of ink in the nozzle opening having ejected the ink droplet has the vibration state shown in FIG. 10. When pressure to ejecting the next ink droplet is applied with a meniscus formed at the outside of the nozzle opening (a region A in FIG. 10), a large amount of ink droplets is ejected at high speed. In particular, when the meniscus is formed at the outside of the nozzle opening immediately after an ink droplet is ejected and then pressure to ejecting the next ink droplet is applied, a larger amount of ink droplets is ejected at high speed.
In order to avoid this phenomenon, a method of supplying no signal for ejecting ink droplets when a meniscus is formed at the outside of the nozzle opening (the region A in FIG. 10) may be proposed. However, the method makes it difficult to realize a high-speed recording operation. In other words, in order to realize the high-speed recording operation, it is effective to start the next printing period even when the meniscus is formed at the outside of the nozzle opening.